Prosthetic limbs for the lower extremities typically include a residual limb socket, an alignment system, and distal prosthetic components to complete the limb. The prosthetic socket is the portion of the prosthesis designed to fit on the residual limb, grasp it securely, and provide the functional connection to the distal components. If the prosthetic socket does not fit properly, it will inevitably be uncomfortable for the patient, even to a level of intolerability. Even the most advanced prosthetic limb components distal to the socket will not serve the patient well, if the socket fits poorly. Ultimately, the prosthetic socket needs to enable the patient to efficiently translate her or his functional intention into functional actuality, by way of the prosthetic limb components distal to the prosthetic socket.
Aside from the universal issues of fit, comfort, and functionality, the amputee population is diverse in many ways, and there is thus a demand in the market for diversity in the types of prosthetic sockets. Diversity in the population of patients follows from conventional demographic variables, such as body weight, age, K-level, and individual levels of activity and personal preferences. It is also common for amputee patients to have more than one prosthetic socket, as well as more than one set of distal prosthetic components, which they use according to the specifics of activity in which they are engaged. The Infinite Socket™ system of LIM Innovations, Inc. (San Francisco, Calif.) is an example of a transfemoral (TF) prosthetic socket that is able to fit many patients, due to its modular assembly, its numerous adjustable features, and its use of thermoplastic fiber composite materials that permit a thermal reforming of components to optimize fit.
No matter how advanced the design, components, or materials, any prosthetic socket still involves a tradeoff between (a) versatility/adjustability and (b) increased complexity, weight, and bulk. A complement to a prosthetic socket with such options as possessed by the Infinite Socket™ system could thus be a socket with a narrower range of adjustable hardware options, but with an overall leaner profile that could be attractive to many patients, as, for example, those who engage in high performance activity.
Protecting the distal end of the residual limb from having to bear the load of the body weight of the patient is a particular challenge in the fitting of a transtibial prosthetic socket. The distal end of an amputated bone lacks the condyle of an intact bone, which, when intact, enables durable and functional load bearing. Thus, it is desirable for a prosthetic socket to spare the distal end of the residual limb from such load bearing by distributing the load elsewhere. In one approach, compression of the socket around the residual limb is helpful, in that it can distribute load away from the distal end of the residual limb and across a larger surface area of the residual limb through points of contact with the socket. In another approach, load can be distributed toward the most proximal region of the socket, where an appropriately contoured brim element can absorb load, transferring it away from the residual limb itself and onto the pelvis.
Still, protecting the distal end of the residual limb from having to bear the load of the body weight of the patient, even if done well, may not fully enable the functional optimization that might be desirably provided by a prosthetic socket. The residual limb is not a monolithic structure; the bones are not firmly locked within muscle like concrete, and the muscles themselves have a degree of movement independence from each other. Compression of the residual limb by a prosthetic socket may create a firmness of the limb as a whole, but it does not transform the residual limb into a monolithic structure. Further, excessive compression is not tolerated well for prolonged periods by patients, and it can bring a host of undesired effects. In addition to challenges associated with load distribution, the transtibial residual limb is missing its former distal portion, which normally acts to provide biomechanically intelligent leverage through that portion of the limb, and to stabilize the position of the upper portion of the limb as it connects to the body through the hip.
Despite the very significant advances made by the Infinite Socket™ system, additional improvements in prosthetic sockets are still being sought. It would be ideal, for example to have a prosthetic socket with improved ability to distribute forces placed on the residual limb as it is hosted within the socket in a biomechanically appropriate and normalizing manner. It would also be ideal to have a prosthetic socket designed for a transtibial residual limb. At least some of these objectives will be met by the embodiments described below.